Mechanical Aptitude Test

[HDRDTD]

I've challenged the Mech engineers where I work to take the test to see just how they scored.

So far only a few have bothered taking it and they came in at 460, 470,480, and me a non-engineer at 410.

There are a couple of questions that have debatable answers, depending on your point of view.

Such as the intake stroke bringing air in. Air pressure is the correct answer but 'suction' should also be correct, by definition.

The fulcrum with the two boxes on it, the left one near, the right one a distance away is another.

If you look at it from a simplistic point of view and you assume the box occupies 2 segments, then the right box is 3 times as far away (the correct answer) but if you compare from the middle of the left box to the middle of the right box, then the ratios appears to be 5:1 not 3:1.

you need to look at the test as an ENTRANCE exam, rather tha as a final examine. Don't make things more complicated than they need to be.

[Joe AutoDrill]

Someone said that suction can't exist without air in the first place. :)

Fun little time waster though, eh?

Regards, Joe Agro, Jr. [phone]

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills:

[HDRDTD]

This one triped up every engineer here that has taken the test so far.

I was thinking along the same lines at first, noting that if you measure from the center of each box to the fulcrum, the the distance ratio appears to be 5:1 but that results in an answer of 60kg, and that ain't an option given.

However....

If you look at it as each box sites on two segments, and count that way, or in other words if each segment was shown as the width of a box, the the ratio appears as 3:1 which provides the correct solution.

[HDRDTD]

Again, this one is debatable as both 'Suction' and 'Atmospheric Pressue' are valid answers.

As the piston goes down, it results in lowering the air pressure inside the chamber. Thus there is now a difference in pressure between inside the chamber and outside. It's this difference in air pressure that results in air flowing into the chamber.

Of course the piston going down creates a lower pressure in the chamber, which results in 'sucking' the air in.

Both answers are correct.

[Gerald Ross]

420. Thought I did better.

[Limey Lurker]

I scored 470

[Dan Coby]

occupies 2 segments, then

from the middle of

examine. Don't make things

I dare you to take a real set of boxes and a real lever and fulcrum and try it. You will not get 100. As illustrated (and assuming that the boxes are homogeneous) the correct answer is 60.

[Swingman]

"Robatoy" wrote

Not being smart enough to make this old box do/allow php, I don't see anything but a banner ad for trucks and diesel parts ... so I guess I fail by default.

Sounds interesting, though.

[Steve]

410 -- not bad for a ex-computer weenie

The one useful thing I got from an education degree was an understanding of testing theory. These guys made the same mistake you see on every standardized test: only ONE selection can be true. Corollary: "All of the above" should never be used. If "All of the above is correct", then all of the other answers are also correct. The test designers try to get out of this by saying, "Choose the most correct answer". But this is equivalent to saying, "Choose the most pregnant woman". An answer is either correct or not.

OK, I feel better now. Thanks for listening.

[B A R R Y]

470

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[Robatoy]

Vacuum is the default. The voids of space are a vacuum. Atmosphere and its pressure are the aberration.

The piston is mechanically pulled down to create a condition akin to a vacuum. The mere presence of an atmosphere allows a flow to occur TO the vacuum. The atmospheric pressure does NOT create a vacuum. In the piston's case, a mechanical event creates a vacuum. The void created by removing atmospheric pressure creates the vacuum, therefore......

[Robatoy]

No they are not. Atmospheric pressure is 14.6 PSIA A little over 14 psi over nothing. Nothing (vacuum) is the default. The downward pull of the piston is created by a mechanical input. (Flywheel, whatever) The atmosphere simply fills that void...it surely does not CREATE the vacuum.

[Robatoy]

I will remain interesting as long as Miller doesn't find a semantic error somewhere by somebody. Nobody throws cold water on warm, fuzzy, cozy discussions like Miller.

[Andy Dingley]

I think this one's reasonable - it's multi-choice, you do know that it's one of the answers, and _only_ one of the answers. With that extra axiom, the answer is clearly "atmospheric pressure" rather than "cylinder suction".

Given what I learned from the balloons question, I think it's actually local variations in non-constant air pressure between cylinders...

[Andy Dingley]

This is a very obvious one -- _if_ you remember that it's for a vehicle company. Bernoulli's principle (the pressure drops if the flow velocity speeds up) is a key part of how petrol carburettors work.

[Doug Miller]

The fan blowing on the fan is an ambiguous question. They're facing each other, and spinning the "same" direction, in the sense that when viewed from the side, they're both spinning down on the edge facing you (or up, depending on which side you're on). But when each one is viewed from *its*own* front, one is spinning clockwise, and the other counterclockwise.

So is that the same direction? Or the opposite direction?

[Doug Miller]

Not "appears to be". Is.

That's because the testmaker screwed up, and forgot that the weights will behave as point masses located at their respective centers of gravity. 60kg is the correct answer.

No, not the correct solution -- the solution that matches their answer.

[Robatoy]

Both blades rotate in the same direction regardless of vantage point. You stand behind one fan, and both blades turn clockwise. You stand behind the other, both blades turn anti-clockwise. What on earth is so hard about that, oh wise one?

[Dan Coby]

You clipped my original posting. Your clipping totally mangles my statements about why I think that this question is ambiguous and my reasons for making the choice that I did.

Yes, I know about Bernoulli's principle and about venturi tubes, carburetors, etc. I took physics long ago (about 37 years) and I do remember Bernoulli's principle.

I said: "This is a venturi tube. The height in tube B will definitely be lower than tube A." If the pressure in the venturi (i.e at the point that tube B is connected) is low enough then there may not be no water at all in tube B. (In this case 'low enough' means less than the ambient air pressure or whatever is the pressure at the top of tube B.)

For example, I have a little device that is used to drain the water from a waterbed. The device is screwed to a faucet and it has a venturi. A hose connects from the middle of the constriction to a waterbed. To use the device, you turn on the faucet and water flows through the venturi and then out of the device. The device makes use of the reduced pressure in the venturi to draw water from the waterbed. (Of course it is high atmospheric pressure which is forcing the water from the water bed. The venturi does not actually 'suck' the water.)

My original post on this issue:

#44. Another ambiguous question. I finally chose C (in tube A only). I had initially selected A (higher in tube A then tube B) but changed to C. As mentioned by another poster. This is a venturi tube. The height in tube B will definitely be lower than tube A. Whether there is any water in tube B depends upon the outlet pressure at the right. I guessed that they wanted C. After I went to the next question. I reconsidered since A would be technically more correct. However getting the answer correctly on a test involves guessing what is expected by the people creating the test. I guessed wrong.

[Tom Veatch]

The current in each branch of the parallel paths will be inversely related to the resistance of the branch and directly related to the resistance of the parallel branch. You can use Ohm's law (E=IR) to derive the mathematical relationship.

If you assume the path through the switch has zero resistance (an OK first approximation) then the current through the lamp would be zero. As the resistance of the path through the switch increases, the amount of current through the lamp would increase.

If you breadboard it, insert a variable resistor in series with the switch. I predict that as you increase the resistance of the path through the switch, the brightness of the lamp will also increase.

Tom Veatch Wichita, KS USA